The present invention relates to a high frequency heating apparatus and more particularly, to a microwave oven or electronic oven equipped with a rotary table or turntable for placing an object to be heated thereon.
A microwave oven which is now widely used essentially includes an oven-defining structure preferably of double wall construction provided therein with a heating cavity or heating chamber having a hingedly supported door which is adapted to selectively open and close an access opening formed at one side of the oven defining structure, and a magnetron assembly for generating high frequency energy so as to heat an object or food material placed within the heating cavity based on the principle of dielectric heating. Some known microwave ovens are further provided with rotary tables or turntables within the heating chambers for rotation together with the objects or food material mounted thereon so that the degree of heating for such objects is made uniform by causing them to move within the heating chambers.
Conventionally, it has been a general practice to provide most microwave ovens with heating chambers of a rectangular hexahedral shape, i.e., rectangular cubic six-walled, box-like configuration, irrespective of the presence of rotary tables, mainly because of the fact that the heating chamber of the rectangular hexahedral shape as described above is advantageous, particularly when the microwave oven is not provided with the rotary table, in that such a heating chamber is readily processed during the manufacture of the microwave oven, while the space within the heating chamber is appreciably increased for efficient use of the microwave oven. The conventional heating chamber of the above described configuration, however, is not necessarily best suited to a microwave oven equipped with the rotary table, since the corner portions at the rear of the heating chamber tend to be idle space with respect to the rotary table, and result in such inconveniences in some cases that the object or food material to be heated may be caught at such corner portions and lock or prevent the rotary table from rotation, thus resulting in burning up the driving source, in the worst case. Furthermore, in the conventional arrangement as described above, especially when a metallic spit or skewer is employed for spitting the food material to be heated, for example, in a barbecue cooking, such a spit mounted on the rotary table together with the food material tends to be brought extremely close to or into contact with walls defining the heating chamber or an inner surface of the door for the heating chamber, to generate an intensive electrical spark discharge therebetween during rotation of the rotary table. Particularly, the door is provide with an observation window formed, for example, by holding a punched metal sheet or wire netting between a transparent plate of synthetic resin and a reinforced glass plate for permitting the food material to be readily observed therethrough during cooking and also for preventing leakage of high frequency energy, and if such a metallic spit is brought close to or into contact with the observation window within the heating chamber during cooking, there is the danger that the glass plate will be damaged or wire netting will be broken due to spark discharge arising from the concentration of a high frequency electric field thereat.
In order to overcome the disadvantages as described above, there has conventionally been proposed, for example, by U.S. Pat. No. 3,467,803, a microwave oven in which the heating chamber is formed into a semi-spherical shape. The above prior art microwave oven, however, has such a disadvantage that when a rotary table is disposed therein, it is impossible to rotate the rotary table smoothly if a tall object or food material to be heated is placed close to the peripheral edge of the rotary table, and therefore, such high objects to be heated must undesirably be placed adjacent to the central portion of the rotary table, and thus the effect of uniformly heating the object through the employment of the rotary table is reduced to a large extent.